Magnetic recording



Dec. l, 1953 Filed May 8, 1948 G.E.BERENS ETAL MAGNETIC RECORDING 3 Sheets-Sheet l DDBQBDBBUQQADBD* INVENTOR.

' Dec. 1, 1953 G. E. Bl-:Rr-:Ns ET AL 2,661,397

MAGNETIC RECORDING Filed May 8, 1948 I5 Sheets-Sheet 2 IN V EN TOR.

ERENS ET AL MAGNETIC RECORDING 5 Sheets-Sheet 3 Filed May 8, 1948 Patented Dec. 1, 1953 UNITED S'I."ATE1S PATENT, OFFICE? MAGNETIC lmcoRnrNG....` s

Gregory E. Berens and Charles Colbert, Dayton, Ohio.,l

ApplicationrMay-; 1948;-S'erial No. Y25,914

2 Claims. (Cl. 17a-F1002) The invention described herein maybe manu--A factred and used by. or 'for the United States Government for governmental purposes without payment to us of any royalty thereon;

This invention relates to recording' devicesfor storing and reproducingY intelligence and the methodof using the same, and more particularly to recording devices utilizing a strip of material lfor the .recording'medium .although not necessarily so limited.

There are certain limitationsv to the use 'ofree cordings. For example, lthe 'top frequency that can `be reproduced isyamong other things, a func-` tion'of` the krelative"speed'between'the' record and 'the lreproducing head.I rIf the relative speed is on the orderof two and-one=ha-lfinchesper second,v then "the upper limit of satisfactory yreproduction= of the Asound is'on the order ofa frequencyioftwenty-'live -hundred` cycles per second;` -This might 'beA4 compared tothereproduetionl or music' over an' ordinary telephone system; It wouldbe betterl for the adequate-"reproductionof music.- if the upper limit -were-iivethousand cycle per second or highen The fidelity of reproductionmay rbe greatly Y improved by increasing the relative speed-ofthe recording -head with respect to the record v and correspondinglyl the l:reproducing head* with respect to the record. If, for example, the irelative speed'is doubled, Ethat is,f`ve incher per second; frequencies `up lto five thousand -per vsecond may `be satisfactorily reproduced. l This 'results in fairlyisatisfactory reproduction 'or music In commercial theatersandmoviesthe rate-of speedV of? the flm that passes through the pro-` jectors-results in satisfactory recording andreproductionibythe use of stationary-heads mount ed in the vicinity of the lm as it is fed through the .projector..A f

Making. recordings on a magneticlm" inr the margimofan 87mm; lmihas noi-.been satisfac' tory .for the reason=that the speed of' the iilm-f is too'l'slovrc.' An 8:1n1m.:lm.travels. through the projector at the fnormal rate of aboutftwo and one-rhall.inches:per rsecond.: .f This speed :maybe increased: or decreased within limits.- 'f rAs stated above,-1two andoneehalfinchesper second is too slow: for satisfactoryreproduction ,ofi music.v

An object of this invention iis-.toprovide a =re cordin'gand reproducingsystem utilizing la-Ymagi netic icoatinglin'alsheet of` material, wherein the recording head., .and the reproducing *head are mounted. for fmovementin a direction opposite to the lldirectioniof movementrfof thefinagneti-c coatinggto therebyprod-uce a relative movement 2y between the recording head or reproducinghead; and the `ilm so'- as to.. result in: satisfactory-reproduction.`

Another object vof .this invention Vis- .to provide a system of magnetic `'recording wherein two or more paralleL: magneticallyinterrupted.. Aseg-V ments offcontinuous magnetic .track are usedfor recording. intelligence, wherein. the segmentsI are recorded successivelyin such-.amanner as to utilize a-ll tracks of. the systemitotherehy .produce a continuous record. v

Another object of:.this. invention is,to,. provide two :or-more magnetic.fstripsuponthe sameysheet of record .material wherein l `the recordings; upon the 'strips are .staggered so'. as i tov be, reproduced successively to.1 produce: aucentinuous record.

Another. obj ect ofi; this ,invention is .to rprovide a pair of magnetic strips or bandsonaillm that are adaptedutor have, recordedzathereon and reproduced therefrornequal length ,staggeredgsegf ments.

Another Yiobject of this invention is zto. provide a pairfoff magnetic tracks. upon a moving-picture lm,1wherein :the fiilm'" moves -throughthe projector at arate of speedftoo slow 'for the desiredzridelity' of reproduction `when .advanced past a stationary recording or reproducingfhead, wherein-the recordl isproducedin staggered segments ofvequal. lengthrand the record .reproduced by means-ofLarotary head having 'iiuxj gaps angularly displaced. and axially.: displaced .by a distance equal to: that hetweenzthe tracks, and traveling iata:speed.-eq.uai.and opposite .to the movement of the film.

' .Anotherobject-'of'thisf 'invention is to: provide a magnetic record wherein :interrupted-.Stripshf track :are used itc produce acontinuous record.

Another Iobjectaof this invention is to; provide a method .for :storing-rand. reproducing intelli-v gence in which the maximum amount-ofintellir gencecan be. storedcin a:m,nimumz0f space, s

Another object .of thisinvention `is to provide a method for storingzandreproducing-intellif gencefin whichamaximum possible iideli-ty'r is achieved.

A further object of this invention is to produce,V a methods for storing-tand` reproducing-iintelli'gence in which ,maximum :playing time. is achieved; i f -A further object of this invention vis -toaprovide a methodf for storing and 4reproducing intelligenceinwhich both increased playing time. and increased .delity' are achieved.' i

Another objectof: this. invent-ion is1to provide a methodior -fstoring .and Ireproducing :intellifpl a method for storing and reproducing intelligence in which greater fidelity can be achieved,

as in sound motion pictures, when the speed of progression of the storage medium cannot be increased.

A further object of this invention is to provide a method for storing and reproducing intelligence in which greater fidelity can be achieved, as in sound motion pictures, wherein the direction of progression of the storage medium canriot be reversed.

Another object of this invention isto provide a method for storing and reproducing intelligence in which wastage of no portion of the storage medium results from lack of foreknowledge of the total playing time required.

A further object of this invention is to provide a method for storing and reproducing intelligence 4in which increased fidelity can be achieved on sound motion picture film by use of multiple i storage paths scanned alternately by recording and reproducing heads made to move in a direction opposed to that of the storage medium.

Other objects and advantages reside in the construction of parts, the combination thereof and the mode of operation, as will become more apparent from the following description.

In the drawings: Figure l is a perspective view of an 8 mm. lm recording or reproducing mechanism utilizing two parallel magnetic tracks;

Figure 2 is a fragmentary view of a lm provided with magnetic coatings which are in actuality continuous parallel, magnetic tracks. The

segmentation shown refers to the sequence in n.

which the signal intelligence is magnetically impressed, as explained below.

Figure 3 is a perspective view of a head at each of two gaps that may be used either for recording or reproducing a magnetic record similar Vto the one shown in Figures 1 and 2. Figure 4 is an enlarged skeleton view showing the mechanism in the recording heads disclosed in Figure 3.

' Figure 5 is a small fragmentary view illustrat- I ing a modified process.

Figure 6 is a schematic showing of a series of recording or pick-up heads shown for the purpose of illustrating the mathematical equations set forth herein.

Figure 7 is a top plan view of the schematic showing in Figure 6, so as to show the offset relation of the several heads.

Figure 8 is another schematic showing used in connection with the development of the theory involved.

In the storage of intelligence for later reproduction, it is important that the greatest amount of intelligence be stored in the smallest amount of space, that the reproduction be of acceptable quality and that editing be facilitated.

In any device for the storage and/or reproduction of intelligence, it is important that the available area of storage medium be utilized to provide the maximum lineal storage path. The

playing time, or amount of intelligence storeable, is inversely proportional to the speed at which the lineal storage path is utilized. The speed at which the lineal storage path is utilized is governed by the relative speed between the path and the recording or reproducing head.

The quality of recording or reproduction is, on the other hand, proportional to the vrelative speed between the path and the recording or reproducing head. It can, therefore, be stated that:

since l L M v l V""P. T.

and VraQ therefore Q V'UP. T.

where Vr isthe relative speed between the 'lineal storage path or track and the recording or reproducing head, P. T. is the playing time of the total available lineal storage path and Q is the quality, or fidelity of recording or reproduction.

-Inrecording and reproducing intelligence, it is desirable that the storage medium progress unidirectionally in order to facilitate editing. ,In some instances, such as in sound motion pictures, it is mandatory that the storage medium progress unidirectionally.

In some devices for the storage and reproduction of intelligence, such as, for example, present single path magnetic tape recorders, part of the available area of storage medium is not utilized, thereby wasting potential lineal storage path, although unidirectional progression of the storage medium is achieved. In other such devices, as, for example, multi-path to-and-fro magnetic tape recorders, available area of storage medium is more fully utilized, but the advantages of unidirectional progression of the storage medium are sacriced. In present sound motion picture films, as well as in single path, unidirectional magnetic tape recorders, the speed at which the lineal storage path is utilized is identical with the speed at which the storage medium progresses.

It is well known that general practice with single storage path, unidirectional magnetic tape recorders is to cause the storage medium to progress past a recording and/or reproducing head which is fixed in position and non-rotating, so that a single, relatively narrow, lineal storage path is scanned by the head. Generally, the total available area of storage medium is not utilized.

It will be seen that if a multiplicity of parallel lineal storage pathswere utilized on the entire available width of the'storage medium, and if one or more rotary recording and reproducing heads, having suitable brush and slip-ring signal pick-offs, were arranged so that the magnetic gaps therein move in a direction opposite to the direction of motion of the storage medium, and the magnetic gaps scan sequentially in regular segments, two or more of the available parallel lineal storage paths, better utilization of the available area of storage medium is achieved. It will also be seen that either longer playing time or greater fidelity, or a combination of both, may be achieved. It will also be seen that unidirectional progression of the storage medium is retained during recording and reproduction.

The. same results; will loe-'achieved if ones-0r more reciprocating. recording and .reproducing heads are arranged so that the. magnetic gaps thereinv move in adirectionoppositefto the direction of :motionot the-storage. medium, soV that 5V these gaps vscan sequentially in regular -'segments two ormorc of the available parallel lineal storage paths. l I i i i In the accompanying drawings, Figure 6 shows a system for recording andreproducing intelli.- 10v gence byI means of rotating y heads designated herein "by the letter h and indicated sequentially by number as h1, h2 and haA of radii r1, rz andra, each having-one lor more1recording and reproducing contact points'or recording elements g1, l5

g2, gse, gab, such Aas magnetic gaps, writingstyli, et cetera, with the letter g herein indicating the word gap and' with numbersvor letters following the letter gindicating reference to particular or different gaps: `The storage medium or Ytape indi- Called in Figs. 6, 7 and 8 by the letter tfor tape is provided with-'magnetic tracks corresponding to the tracks 'I4 and i6 on the storage medium lil in Figs. l and 2. Each ux gap g1, g2, gas and gib in Fig. 6 records in anyv desired coordinated se- 25l quence. As indicated in Figs; `6 and 7 gap gris assigned'to one track, gap g2 is assigned to a different track, and gaps gas and gab are assigned to a still diie'rent track, Storage medium tape t is passed over each head in a direction shown 3U' opposite to the direction of rotation of such heads and making angles of'contact or of wrap therewith ofl magnitudesdesignated as 01, 02 and 03,. where the symbol (9v-indicates an angle of, wrap and@ followed by a number or a letter indicates reference to a particular angle of wrap on a particular head. Heads h1, he and-h3 rotate with peripheral speeds indicated by the letter v as v1, m and Us, respectively.

In 'Figure '7 head h2 is shown at one extreme 40 of thel storage mediimnand hir-is shown at a position between Vthe extremesand he is shown at the opposite extreme. The positionsof'lheads' h1, h2 and ha coincide with the positions of selected storage pathsl or tracks on the storage medium. In Figures 6 and? three heads h1, h2 and h3 are shown, .althougha greater or lesser number of suchiheads and. corresponding lineal storage paths or tracks mayfbe utilized. There shall be one track assigned to each head. In the gaps onhead h1 being g1, of. whichonly twoadlaY cent gaps .gia and gib are shown separated by an angle of separation Storage medium t passes over an arc on head hx making an angle of contact @i at speed v, ina direction opposite to'that of motion of the head hi. Length L is. the segment of lineal storage path scanned. by a single gap in the time such contact point sweeps out the angle 01 along the arc thereof. Y.

It isVv clear,4 therefore, that Figure 8 represents the ith head of a general system of n headssimie lar to the system shown in Figures 6 and 7, where the general number n is three.

It can be shown that,rfor maximum utiliza-` tion ofeach and .every lineal storage pathor track in a system of` n heads, the relationships between the variables considered herein as apf plied to the assemblages shown in the accom* panying drawings and particularly in Fig. 8 may be expressed as follows:

where V is the speed of the lm or tape t, and Vi is the peripheral speed of the z'th head, ci.l is the angle swept by a gap on the ith headl and ci is the number of gaps on the ith head.

i=n 23a-@azar A (2) z= where L is the length of nlm or tape scanned by a single gap g in the time the gap g sweeps out the angle 0i of the head h1.

an auxiliary equation is:

Table of edivalent elements For- Element Fig. Ele- Fig. Elc- Fig. 'F No' Element No. ment No. ment rt;-

VDescription Element Element Trne, storage medium, l 10 6 i m. Traoks, lineal storage 1 14,16 2 14, 1 6 I partira-bands. No. of tracks Heads 28 represents 2 eads. No. of heads Gaps No. ci gaps Ourthe ith heady Angle of contact, angle of wrap.

Length of segment Radius oi'ith head Speed ofthe ith head..." Speed of the tape general system the number of heads is designated as the number ln.

In Figure 8 ahead yhx is shown of radius ri,

rotating at peripheral speed vl the number of 7 Referring to an illustrative embodiment of the invention as shownin the drawings, the retenence` character lil indicates aiilm which may be 5 a conventional 8 mm. nlm, provided with pin feed apertures I2 normally used in feeding the lm t-hrough the camera and for feeding the lm through the projector. This film is provided with two tracks I4 and I6 of .magnetic material applied to the film in any suitable manner.

In view of the fact that the relative movement of film through projectors for home use is too slow for prop-er recording and reproducing by use of a stationary head and single track, two tracks or bands of magnetic material have been provided to be used in conjunction with a twogap rotary head. The two bands are recorded in staggered segments in such a manner that the recordings are made upon segments of each band alternately and reproduced alternately, to provide thereby a continuous recording that progresses along both bands in alternate steps, so as to permit the utilization of a track length equal to twice the length of the lm. A rotary head is used, the gaps of which move at a speed equal to and opposite to the movement of the film, thus doubling the relative speed between gaps and track. This device records and reproduces the segments on the bands alternately. The length of the segments is a function of the length of the effective stroke of the pick-up head or heads and of the relative speed between gaps and track.

Again, referring to the drawings, the successive segments on each side of the iilm have been referred to by lettered subscripts Illa to lh and Ilia to |671. For convenience in description, the segments have been separated by blank spaces I8. in actual usage, the two bands will be continuous, the recordings on the segments being momentarily interrupted at the areas Corresponding to the blank spaces.

In making the recording, the segment Ilia, only a portion of which has been shown, is first recorded. Then the segment Ilia is recorded. This is followed by a recording upon the segment I4b, the film moving downwardly, as viewed in Figure 2, and the recording mechanism, which will be described morefully later, moving upwardly. After the segment Mb has been recorded, the segment |61) is recorded, opposite segments being recorded alternately, the segments being arranged in staggered relation, as shown in Figure 2. For

purposes of providing proper registry of the nlm with respect to the recording and reproducing mechanism, ends of each segment register in a predetermined manner with respect to the pin feed apertures I2 in the ilm or strip, as is also shown in Figure 2.

, One or more heads having two or more gaps may be used in recording on the tracks. Furthermore, heads may be mounted for rotary or reciprocatory movement.

In Figure 1 the rotary method of recording and reproducing a film has been shown schematically. The mechanism includes a pair of constant speed sprocket wheels 2i) and 22. The lm is fed over the sprocket wheel 2U, then downwardly between rollers 24 and 26 around recording or pick-up heads 28 and up over the sprocket wheel 22. The heads 28 also are shown in Figs. 3 and 4. The two sprocket wheels 2B and 22 are driven by a suitable mechanism not shown.

The recording or pick-up heads 28 are mounted upon a shaft 30 rotating in a direction opposite to the direction of movement of the lm. The peripheral speed of the recording or reproducing heads 28 is the same as the speed of the nlm.

Furthermore, the circumference of a head is equal to a length of a segment, as will appear more fully later.

Fig. 3 shows two heads mounted on one geardriven shaft, which is common to both heads. Fig. 4 is an internal detail view of Fig. 3. The head consists essentially of coils and associated magnetic laminations. The recording, pick-up, reproducing or magnetic head 28 contemplated hereby and illustratively shown in Fig. 4, is in actuality two heads each having one gap, each head, and consequently each gap, in this case, being assigned to one track. The laminations associated with one half of the magnetic path are indicated as 40, 50 and 46. The laminations associated with the remaining half of the magnetic path are indicated as 42, 52 and 44. The assemblage shown in Fig. 4 within a dash-line is inclosed within the cylinder shown in Fig. 3. The flux gaps 48 of Fig. 4 are indicated as correspondingly positioned open gaps in the cylinder in Fig. 3. Flux gaps 48 in Fig. 4 are elements similar to the flux gaps in Figs. 6 and 8. Each iiux gap 48 is energized electrically from the brushes 'I0 and 12 and maintains a magnetic flux within the field of which a track of the nlm I0 or tape t passes as it wipes against the cylinder in Fig. 3. The film moves in a direction opposite to that of the cylinder. The relative speed between the flux gaps and the lm is twice the film speed. As is well known to those skilled in the art of magnetic recordings and reproductions, each group of magnetic laminations is arranged in spaced relation so as to provide a flux gap 48. The magnetic members 50 and 52 support the coils 54 and 56. The coils 54 and 56 are connected in series by a lead 56 and connected to the slip rings 60 and 62 by means of leads 64 and 66.

A pair of brushes 10 and. 12 are connected into a suitable circuit either for energizing the coils or for amplifying the signal picked up by the coils in response to the magnetic iiux linking the air gap of the magnets.

As far as the explanation of the principle of operation is concerned, the structure described thus far may be used either for recording or for reproducing the signals. The pin feeding wheels 20 and 22 and the recording or reproducing mechanism 28, which may be referred to generically as a magnetic head, are driven from a common source such that the velocity of the film is preferably equal to but in opposite direction to the peripheral velocity of the magnetic head. The mechanism for driving these parts has not been shown for the reason that any suitable driving mechanism may be used.

For convenience of explanation, let it be assumed that one gap is located in the position designated by the reference character in Figure 1. The other gap would then be located under the roller 26 in the position 82. Furthermore, let it be assumed that the film and the magnetic head 28 rotate and move in the directions of the arrows shown in Figure 1. From this it may be readily seen that the magnetic head in the position 80 is leaving or moving out of contact with the magnetic track I6 and at the same instant the other magnetic head in the position 82 is moving into contact with the magnetic track I4.

From the foregoing it can readily be seen that the distance between interruptions in the recording of the opposite tracks I4 and I6 is equal to con ener-half of the circumference of the head, v rtliermoraitali ,ieasiilrre @e that the @1min ,with the, head extends aref er1 er@ .S1-ibteadiee ansie @480 f tagged, as im in Figure 1. In `the' event thearea in conta-ct with the head is less than 180", there would be a short nteryailwhen the recording or the reproduction, @estrie @estimar ha ireuldibeinterruntedl -Ifthe area in contact with the pick-up head is more than 180, there may be a slight overlap. By causing the film to travel at a velocity slightly greater than the peripheral velocity of the pickup head, the recording and reproduction may be continuous without overlapping the previous recorded segment. From the foregoing, it can readily be seen that the segments will be alternately recorded or reproduced, as the case may be, first the segment along the band or track ld, this followed by a like segment along the band I6, then back again to the succeeding segments of the band I4, et cetera. By this arrangement, the desired relative velocity may be doubled with respect to the movement of the nlm.

Instead of utilizing two tracks, one along either margin of the film, one track of approxin mately double width may be used. The tracks in the preferred embodiment have been shown on the broad side of the film and on the same side. Instead of being positioned on the broad side of the film, the magnetic applied on the edges of the nlm.

Furthermore, the tracks may be located on opposite faces of the iilm, as for example, the lm disclosed in Figure 5. In this modification, the lm is coated with a magnetic track or strip |02 applied to the margin opposite the margin containing the pin feed holes |64. On the opposite side of the film is a magnetic band |05 located between the pin feed holes and the outer margin of the lm.

The feeding mechanism for feeding the film has not been shown in Figure 5; but the lm may be fed in such a manner that the magnetic coating strips or bands |02 and |08 pass along parallel paths. A magnetic head |08, shown schematically, is actuated along the path lit in the direction of the arrows so that the magnetic head |08 moves in the direction opposite to the direction of movement of the film. First the magnetic head moves in the direction opposite to the direction of the iilm, along the magnetic band |02, then when it comes to the extreme right position of the arrowed lines, the magnetic head is transferred so as to overlie and travel along the magnetic band |06 traveling towards the left, this portion of the lm traveling towards the right, until the magnetic head comes to the extreme left end of the arrowed lines, when the magnetic head is again suddenly transferred so as to overlie the band |02. The mechanism for actuating the magnetic head and for actuating the nlm has not been shown, as any suitable actuating mechanisrn may be used.

Instead of utilizing one reciprocatory head, two reciprocatory heads may be used. Furthermore, instead of using two rotary7 heads, as shown in the preferred embodiment, a single rotary head may be used by merely causing a relative axial movement between the magnetic head and the film when transferring from one segment to another. In other words, various types of devices may be used for causing a relative speed between the magnetic head and the film that is greater than the speed of the film.

coating material could be :l

scribed 269i 11.15

altri-thin? l0 :instead ef patria tarea er mere @wld te use@ om ish the same result.

declared tangier has-been iis- .1.1 a magnetic elm for recording signal intelligence. The same `prinipule might .be

` g and-reproducing optical sigle, Asignals used in sound recordings n pictures, wherein the inten- Siirei the Ahaar is --variedtr thereby eener-aie a uwafie pulsating Carrear l' Althoughthe preferred'embodiment of the devicehas' been described, it-Will be understood that .thef' purview of .thgis'zinventioh =yarious changes may be made in the form, details, proportion and arrangement of parts, the combination thereof and mode of operation, which generally stated consist in a device capable of carrying out the objects set forth, as disclosed and defined in the appended claims.

Having thus described our invention, We claim:

1. A strip recording mechanism for recording intelligence along a plurality oi parallel paths on a strip storage medium, comprising a pluralty of cylindrical recording heads having equal radii and rotated by a common shaft, the number of heads being equal to the number of parallel paths, each head having on its periphery at least on recording element adapted to impose a record on the storage medium and to provide a magnetic ilux gap with the magnetic flux gaps connected in a common magnetic circuit, means for moving the strip storage medium in one direction at a constant linear speed substantially in contact with each head over a predetermined arc, means for rotating each of said recording heads at a constant peripheral speed in a sense opposite the direction of storage strip movement, the variable factors of said mechanism being so selected that the sum of the products or" the number of recording elements on each head times the predetermined arc of contact oi' the storage strip with the respective head expressed as an angle in radians shall equal 2 pi, and for each cylindrical recording head the ratio of the speed of the storage strip to the peripheral speed of the respective cylindrical head shall equal the product of the number of recording elements for the and the arc of contact of the 2. A pair of magnetic heads, comprising a cysecond axial end of said cylindrical surface and the first and second ux gaps being positioned i1 a at diametricai opposite edges of said cylindrical Number surface, a pair of magnetic members joining said 1,825,441 rst to said second pair of laminations, a coil 2,195,701 on each of said pair of magneticvmembers, and 2,352,023 means for energizing said coils. 5

GREGORY E. BERENS. Number C ARLE ER H s COLB T 331,576

References Cited in the le of this patent UNITED STATES PATENTS 10 Number Name Date Cawley Sept. 29, 1931 Name Date Cawiey Sept. 29, 1931 Kent Apr. 2, 1940 Schuiier June 20, 1944 FOREIGN PATENTS Country Date Great Britain July '1, 1930 

